In September 1936 Yezhov replaced Yagoda as the head of the NKVD. More than any other police chief, Yezhov was prepared to indulge Stalin's paranoic fantasies by fabricating evidence of 'counter-revolutionary conspiracies' and 'spy rings' everywhere. He had curried Stalin's favour by uncovering the Kremlin Affair in 1935.

For several years, Yezhov had promoted the theory that, on Trotsky's orders from abroad, Zinoviev and Kamenev had been plotting to murder Stalin and other members of the Party leadership, including Kirov. On this basis, Stalin reopened the Kirov investigation. In August 1936, Zinoviev, Kamenev and fourteen other Party leaders were put on trial for treason. All of them were sentenced to death, along with 160 other people arrested in connection with the trial.

This was the first of several 'show trials' during 1936-38. Their aim was to expose a coordinated ring of 'spies' and 'terrorists' organized by former oppositionists. It was not enough to convict and punish them: the aim of the show trials was to prove the existence of these 'conspiracies' beyond doubt by having the accused confess their guilt before the Party and the world (unaware of the torture used to extract their confession). In NKVD circles the confession was regarded as the highest form of proof. There was no other evidence.

Zinoviev's prison photos

A second show trial, in January 1937, witnessed the conviction of Piatakov, Radek and fifteen other former supporters of Trotsky for industrial sabotage and espionage - as already proven by the Kemerovo trial.

In April-May 1937, eight of the country's senior military commanders, including Marshal Tukhachevsky (Deputy Commissar of Defence), General Uborevich (Commander of the Belorussian Military District) and General Yakir (Commander of the Kiev Military District) were arrested, tortured brutally, and tried in secret for treason and espionage. It was said that they were financed by the Germans and the Japanese. All of them were shot on the same day.

In the last and biggest of the show trials, in March 1938, Bukharin, Yagoda and Rykov, along with thirteen other senior officials, were sentenced to be shot for conspiring with the Zinovievites and Trotskyists to assassinate the Soviet leaders, sabotage the economy, and spy at the behest of the Fascist powers. Yagoda's involvement in the plot supposedly explained why it had taken so long to uncover it.

In all these stage-managed public trials - in which the accused were meant to speak the words scripted for them by their torturers - Stalin played a directing role behind the scenes. The death sentences given to the convicted had been decided by the Politburo beforehand.